Source : Free On-Line Dictionary of Computing

ZX-81
     
         An even more successful version of the {Sinclair}
        {ZX-80}, featuring a large {uncommitted logic array} instead
        of much discrete logic, an improved {BASIC}, and rather more
        expandability (it could take 16kb {RAM} packs).  It was
        launched around 1981 and was eventually replaced by the
        {Spectrum}.
     
        (1995-11-04)